A wireless power transmission or a wireless energy transfer refers to a technology of wirelessly transferring electric energy to desired devices. In the 1800's, an electric motor or a transformer employing the principle of electromagnetic induction has been extensively used and then a method for transmitting electrical energy by irradiating electromagnetic waves, such as radio waves or lasers, has been attempted. Some electric toothbrushes or wireless razors, which are usually used, are actually charged with electricity through an electromagnetic induction principle. The electromagnetic induction refers to a phenomenon in which a voltage is induced so that a current flows when a magnetic field is varied around a conductor. Although the commercialization of the electromagnetic induction technology has been rapidly progressed around small-size devices, the power transmission distance thereof is short.
Until now, the long-distance transmission using the electromagnetic induction, the resonance and the short-wavelength radio frequency has been used as the wireless energy transfer scheme.
Recently, an energy transfer scheme has been extensively used based on an electromagnetic induction or resonance scheme among wireless power transmission schemes.
Since a wireless power transmission system based on the electromagnetic induction scheme and the resonance scheme wirelessly transmits electrical signals generated from a transmitter and a receiver through a coil, a user can easily charge an electronic device such as a portable device with electricity.
However, the power transmission efficiency of the wireless power transmission system may be degraded due to an unnecessary frequency component of AC power supplied to a conventional wireless power transmitting apparatus.